This invention pertains to apparatus and methods for separating or chopping, such as cutting, shearing or breaking long or continuous things like fiber, strand, ribbon, tape, etc. into short lengths and is an improvement in the prior art apparatus and methods for so separating such long or continuous things. The invention is particularly useful for separating long or continuous strands made up of individual fibers of glass, ceramic, mineral or organic polymer into short segments such as up to 3 inches or more in length. For example, fibers are pulled from molten glass, molten polymer, etc. flowing through a multitude of holes or nozzles in a high temperature bushing to form one or more strands. Some products require separating these fibers or strands of fibers into short lengths. Glass, mineral or ceramic fibers are particularly hard to separate because of their hardness and abrasiveness.
Things like fiber, ribbon, tape, etc. and strands made up of a plurality of one or more of these or similar things, are typically made in continuous form or in long lengths. Continuous, as used here, means very long lengths such as more than a hundred feet long and typically includes things that are thousands of feet and even miles long. Such things, such as fiber and fiber strands, must be separated into short lengths, typically between about 0.16 up to 3 inches or longer. The fibers often are very hard to separate into smaller lengths due to their hardness and/or toughness and/or due to one or more chemicals on their surface, placed there to protect the surface, and which often contain a lubricant.
Apparatus currently known for separating or chopping are designed to operate to work product speeds of hundreds and often thousands of feet per minute. Often the capability of this apparatus is the limiting item in the operating speed of the entire manufacturing process for making the chopped product. Also, when chopping, the working parts of the apparatus wear or distort to the point that the separations are incomplete which is unsatisfactory because the incompletely chopped items, such as fiber strands, are defective and often cause defects in the application in which they are used.
Typical apparatus for, and methods of, separating or chopping, as described above are disclosed in U.S. Pat. Nos. such as
3,508,461 3,731,575 3,744,361 3,815,461 3,831,481 3,869,268 4 043,779 4,045,196 4,083,279 4,175,939 4,237,758 4,248,114 4,287,799 4,344,786 4,347,071 4,367,084 4,373,650 4,398,934 4,411,180 4,528,877 4,576,621 4,615,245 4,637,286 4,706,531 5,003,855
Many of the apparatus and methods disclosed in these patents use an elastomer, thermoplastic polymer or other temperature sensitive materials in one or more key components of the chopper apparatus, such as the back up or cot roll, the blade holder, blade snugger, blade roll, etc. These temperature sensitive components, such as polyurethane, are frequently used because of their elastomeric characteristics at room temperature or assumed operating temperatures; and thus, the hardness of the component, usually critical, is specified to be within a certain range for best performance. As used herein the term chop, or derivatives thereof, are intended to mean separating the work product into shorter lengths regardless of how such separation is accomplished.
A chemical composition or mixture, usually in aqueous form, referred to as sizing, is typically applied as a coating on the fiber before the fiber is chopped. Sizings compositions exist which produce substantially improved fiber products compared with existing products, but they are impractical because they make the strands of fiber so difficult to chop that they are commercially unfeasible.
When trying to chop the hardest-to-chop fiber strands at speeds exceeding a thousand feet per minute, often at speeds exceeding 2500 or 3500 feet per minute, the blade roll frequently fails. Such failure may cause sharp blades to fly off the blade roll causing a serious safety hazard and a costly shut down. Also, when chopping the most difficult to chop strands, the blades and temperature sensitive portion of the back up or cot rolls always must be replaced after much shorter operating periods than when chopping easier-to-chop strands. For example, normally glass fiber intended for making nonwoven mat using a wet laid process are much easier to chop than glass fiber intended for reinforcing thermoplastics parts made by injection molding. Also, larger diameter glass fiber such as 16 micron is easier to chop than fine diameter such as 10 micron.
It had been delivered that the shorter component life was due only to wear. The stands, etc. are usually chopped in the presence of ambient temperature water, and the rapidly turning blade roll, back up or cot roll, and moving strand(s) move a lot of ambient air around the chopping zone. Thus, it had not been realized that a heat build up was occurring that could affect the components in a way to reduce the effectiveness of the chopping function or process and to reduce their life and cause them to fail catastrophically.